Atomisation of a precursor into an excitation medium for coating a remote substrate

ABSTRACT

The invention relates to a method and apparatus for applying and forming a coating on a substrate surface by the application of at least one atomized coating forming material onto the substrate to form the coating. The atomized coating forming material, upon leaving a suitable atomizer which can be an ultrasonic nozzle or nebulizer for example, passes through an exciting medium and, upon leaving the exciting medium, passes to the substrate. The substrate is positioned remotely from the exciting medium.

BACKGROUND OF THE INVENTION

The invention to which this application relates is to the application ofa coating to a substrate involving the improved utilisation of anexciting medium.

The use of excitation mediums is known in the application of coatings.However, deleterious effects of high energy species can be presentwithin the “exciting medium”, such as bombarding ions and UV photons.This can prevent the coating of sensitive substrates with films thatretain a significant degree of monomer functionality and can also causeion etching effects.

The exciting medium tends to be the medium in which, conventionally, thesubstrate to be coated is positioned. The exciting medium can begenerated in a number of ways, the most common of which is thegeneration of a plasma, with the area over which the plasma is said toextend typically defined by a plasma glow typically Iying within thearea defined by the electrodes used to generate the plasma. Thepositioning of the plasma within the exciting medium is typicallyreferred to as direct PECVD as defined in the book “Cold Plasma inMaterials Fabrication—Alfred Grill—IEEE Press 1993”. The same book alsodescribed the provision of remote PECVD, in which the substrate to becoated is removed from the exciting medium. However in both cases thecoating is achieved through the introduction of gaseous materials andthis slows the deposition rate significantly and renders the samecommercially unviable for many applications.

It is also known from earlier patents such as U.S. Pat. No. 5,451,260and WO9810116 that the substrate can be positioned in the same CVDreactor as a nozzle for introducing material for the coating process butneither patent acknowledges the possible use of atmospheric-pressureplasmas, pulsed plasmas and continuous processing.

The patent application WO 0228548 describes a direct PECVD process,wherein in the examples of the invention, the sample to be coated isplaced within the plasma and hence the exciting medium formed fromatomised coating forming material. In addition the patent applicationdoes not mention low-pressure or pulsed plasmas or other types of remoteplasma and the possibility of non-ionised or non-plasma excitationsources (such as ozone, radicals, UV irradiation or heat). Furthermorein this patent application the nozzle for introducing the coatingmaterial is positioned at the plasma region to introduce the materialwithin the plasma and directly impinges upon the substrate.

Patent application WO 0070117 does not use an atomiser but does useplasmas (high and low pressure) to deposit coatings on a remotesubstrate. However, the pressure range specified in claim 15 (10-1000Torr) is 10 to 100 times higher than that normally used for low-pressureglow discharge deposition, no alternative means of excitation arementioned and no specific examples of polymeric coatings and their usesare cited.

The aim of the present invention is therefore to provide a means ofusing an atomiser to inject a liquid or liquid/solid slurry into anexciting medium to allow rapid deposition, even from involatile monomersonto substrates or a substrate to be coated with improved depositionrates and coating quality so as to render the same commercially viable.

SUMMARY OF THE INVENTION

In a first aspect of the invention there is provided a method fordepositing a coating, said method comprising the steps of; introducingan atomised coating forming material into an exciting medium, saidatomised coating forming material passing through the excitation mediumand depositing the activated atomised coating forming material onto asubstrate, characterised in that said substrate is positioned remotelyfrom the exciting medium.

Typically said substrate is substantially unaffected by the excitingmedium.

This method avoids excessive damage to the substrate or coating appliedthereto from occurring.

Preferably the substrate is sufficiently remote from the exciting mediumsuch that the exciting medium has no or minimal effect on the coatingapplied or the substrate itself. It should be appreciated that thedegree of remoteness can be selected in accordance with operatingconditions and that while there may still be some deleterious effectfrom the exciting medium the purpose and achievement of the invention isto ensure that such effect is minimised so as to be negligible.

In one embodiment the substrate is remote from the exciting medium inthat it is physically spaced from the exciting medium by a selecteddistance and/or a physical obstacle such as a baffle or bend in aconnecting passage is provided and/or a device is provided to removeundesirable, damaging species from the exciting medium and prevent thesame from reaching the substrate. In one embodiment such a device is anelectrically biased or earthed grid positioned between the excitingmedium and the sample.

In one embodiment, additional materials are added to the flow ofatomised coating forming material at, prior to, or subsequent to, theexciting medium.

Preferably said additive materials act as buffers required to maintainprocess pressure and/or carry the atomised coating forming materialthrough the exciting medium to the substrate.

In one embodiment the additive materials have the additional capacity tomodify and/or be incorporated into the coating forming material and/orthe resultant coating.

In one embodiment, in order to produce a substrate possessing amulti-layered coating, the introduction of species additional to theatomised coating forming material is pulsed.

Typically the exciting medium is a plasma discharge

In one embodiment the plasma is operated at atmospheric, sub-atmosphericor low-pressure and can be produced by audio-frequencies,radio-frequencies, microwave-frequencies, or direct current voltage.

In one embodiment the plasma discharge is generated by an alternatingcurrent voltage.

In one embodiment the exciting medium comprises species generated by aremote plasma. Plasmas suitable for such a purpose include, but are notlimited to, atmospheric, sub-atmospheric or low pressure dischargesgenerated by low frequency, radio-frequency or microwave-frequency powersupplies and hollow cathode devices.

In one embodiment the exciting medium is created by a flux ofelectromagnetic radiation such as UV light or y-radiation, oralternatively, a flux of ionised particles such as ions, electrons ora-radiation, or yet further by a flux of radicals. In a furtherembodiment, the exciting medium is generated by a source of highlyreactive species such as ozone.

In a yet further embodiment the exciting medium is created by theinterposition of a heat source, such as a heated grid or heat lamp,between the source of atomised coating forming material and thesubstrate.

In one embodiment the exciting medium is generated by more than one ofthe excitation means, whether singly in succession, in simultaneouscombination, or in a succession of combinations.

In one embodiment the exciting medium is applied continuously.

In an alternative embodiment the exciting medium is pulsed. Suitablemeans of achieving this include, but are not limited to, electronicallypulsing the means of generating the exciting medium (for example, theplasma power supply) or using a shutter to modulate the flux of incidentexcited species (photons, remote plasma species). The operation of ashutter may be mechanical or otherwise. For example a suitablymodulated, electrically biased grid may act as a shutter for theexclusion of charged particles. The pulsing of the exciting medium canresult in a coating that significantly retains the chemical propertiesof the atomised coating forming material.

Thus in a further aspect of the invention there is provided a method ofproducing a multi-layered coating wherein the substrate is repeatedlyexposed to excited coating forming material as herein described, instages. In one embodiment the type or composition of the coating formingmaterial introduced is altered between coating stages.

In a further aspect of the invention there is provided a method ofproducing a multi-layered or graduated coating upon a substrate whereinthe composition of the precursor and/or the nature of the excitingmedium are changed during the production of the coating.

In one embodiment the substrate is coated continuously by use of areel-to-reel apparatus. In one embodiment the substrates is moved pastand through coating apparatus acting in accordance with this invention.

In whichever embodiment, the coating formed on the substrate can bepost-treated by exposure to an exciting medium.

In whichever embodiment the substrate onto which the coating is formedcan be cooled, treated or kept at ambient temperature.

In whichever embodiment the substrate can be pre-treated by exposure toan exciting medium prior to coating.

The substrate can comprise, but is not limited to, metal, glass,semiconductor, ceramic, polymer, fabrics, woven or non-woven fibres,natural fibres, synthetic fibres, cellulosic material, and/or powder.

The coating forming material may constitute, but is not limited to, anorganic, organosilicon, organometallic, or inorganic material, ormixtures or combinations of the same.

The coating formed can be such as to improve the hydrophobic and/oroleophobic, adhesive, gas barrier, moisture barrier, release, electricaland thermal conductivity, dielectric, optical, biomedical,biotechnological and tribological properties of the substrate.

In one embodiment the coating material introduction means is anatomiser. In one embodiment the atomiser is an ultrasonic nozzlesupplied with coating forming material in the form of a liquid orliquid/solid slurry. In another embodiment the atomiser is a nebulizersupplied with coating forming material in the form of a liquid orliquid/solid slurry, and a carrier gas which may be inert or reactive.Yet further the atomiser can be a plain-jet gas blast atomiser suppliedwith coating forming material in the form of a powder, and a carrier gaswhich may be inert or reactive.

Typically more than one atomiser is used to supply coating formingmaterial to the energetic medium.

If required, the excitation medium and surrounding apparatus are heated.

The method can, in whichever embodiment, result in a coated substratewhich is subject to subsequent derivatization by methods known in theart (e.g. tethering of biomolecules).

In a further aspect of the invention there is provided a method fordepositing a coating, comprising a source of atomised or nebulizedcoating forming material (such as an organic or organo-silicon monomeror oligomer) which is introduced into an exciting medium thatfacilitates the formation of activated precursor species to the coating(such as monomer radicals, ions or oligomers), which precursor speciesare subsequently deposited onto a substrate, situated outside of theexciting medium, forming the coating.

The remote placement of the substrate prevents the high energy speciesthat constitute the exciting medium from causing excessive damage to thesubstrate and the growing coating.

In a preferred embodiment of the method, the coating forming material,either a liquid or a solid/liquid slurry, is atomised by an ultrasonicnozzle into an excitation zone and heated to prevent condensation. Othermeans of atomising the coating forming material include, but are notlimited to, nebulizers and plain-jet air blast atomizers.

The exciting medium may comprise the atomised coating forming materialin the absence of other materials or mixed with, for example, an inertor reactive gas. The additional material may be introduced continuouslyor in a pulsed manner by way of, for example, a gas pulsing valve.

In all cases the means of activating the coating forming material priorto deposition would damage the substrate and/or growing film if applieddirectly.

A means of isolating the substrate from the deleterious effects ofdirect exposure to the exciting medium is provided to ensure that thedistance between the excitation medium and the substrate is sufficientto largely preclude damaging phenomena (usually ion bombardment).Another means of achieving this separation is to interpose a physicalimpediment, such as a baffle or bend, between the excitation medium andthe substrate. Alternatively, a device that selectively removesundesirable, damaging species may be used. An example of such a deviceis an electrically biased or earthed grid between the exciting mediumand the sample.

Multi-layer coatings can be produced by a variety of means; namely,pulsing the atomisation source, pulsing the introduction of reactive,additive species to the excitation medium (e.g. intermittently addingoxygen to a plasma); pulsing the excitation medium (e.g. alternatingbetween continuous and pulsed plasma to produce alternating cross-linkedand well-retained layers); changing the nature of the excitation medium(e.g. from plasma to UV); changing the composition of the coatingforming material, and performing multiple treatments (with one or moreapparatuses).

In a further aspect of the invention there is provided a method ofapplying a coating to a substrate, said method comprising the steps ofintroducing into a vacuum chamber an atomised coating material,directing the coating material introduction towards and through anexciting medium to excite the coating material, and characterised inthat the substrate to be coated is positioned with respect to theexciting medium and means for introducing the coating material such thatthe coating material leaves the exciting medium and continues a distanceafter leaving the same to apply to the substrate to form the coatingthereon.

In a preferred embodiment the means for generating the exciting mediumis controlled to ensure that the exciting medium does not extend to thesubstrate so as to have any significant effect thereon.

In a yet further aspect of the invention there is provided apparatus forthe formation of a coating on a substrate, said apparatus comprising avacuum chamber, means for holding the substrate in the said chamber,means for introducing a coating material into the chamber, and means forgenerating an exciting medium within said chamber and characterised inthat the means for introducing the coating material is positioned to beat a first side of the exciting medium when generated in the chamber andthe substrate is positioned to be at the opposing side of the saidexciting medium and remote therefrom such that the directed atomisedcoating material passes through the exciting medium and, upon leavingthe same, passes to the substrate to form the coating thereon.

In one embodiment the means for generating the exciting medium is spacedfrom the location of the exciting medium within the chamber.

In one embodiment the substrate is moved through the vacuum chamber inan in line manner.

In one embodiment the apparatus can be provided as part of a purposebuilt machine or alternatively, some or all of the components of theapparatus can be provided in a modular form to allow the same to beretrofitted to existing coating apparatus in the required configuration.

Typically the means for introducing the atomised coating material isconnected to a supply of the coating material so as to allow thecontinuous and monitored supply of the coating material in the atomisedform and with sufficient velocity to ensure that the material reachesthe substrate to form the coating thereon.

Typically the velocity of the atomised coating material can becontrolled by varying the system pumping speed or gas flow rate toensure that the material reaches the substrate to form a coatingthereon.

Typically control means are provided for the coating materialintroduction means, exciting medium generating means and position of thesubstrate to ensure that the same are adjusted and set to suitparticular operating conditions and to remove or minimise any effect ofthe exciting medium on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following detailed description ofthe preferred embodiment of the invention will be better understood whenread in conjunction with the appended drawings. It should be understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown herein. The components in the drawings arenot necessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

The invention may take physical form in certain parts and arrangement ofparts. For a more complete understanding of the present invention, andthe advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying drawings.Specific examples of the invention are now described with reference tothe accompanying drawings wherein;

FIGS. 1 a and b illustrate a plasma discharge ignited and a source ofatomised coating forming material;

FIG. 2 illustrates a further embodiment of exciting the atomised coatingforming material in accordance with one embodiment of the invention;

FIG. 3 shows a diagram of an apparatus that uses a radiofrequency plasmato generate the exciting medium and effect the deposition of an atomisedcoating forming material.

FIG. 4 is a graph showing the infrared absorption spectrum of 2hydroxyethyl methacrylate polymerised using the method of the invention.

FIG. 5 shows a diagram of an apparatus that uses a remote microwavefrequency plasma to effect deposition of an atomised coating formingmaterial in a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention has been described with reference to specificembodiments, these descriptions are not meant to be construed in alimiting sense. Various modifications of the disclosed embodiments, aswell as alternative embodiments of the invention will become apparent topersons skilled in the art upon reference to the description of theinvention. It should be appreciated by those skilled in the art that theconception and the specific embodiment disclosed may be readily utilizedas a basis for modifying or designing other structures for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

It is therefore, contemplated that the claims will cover any suchmodifications or embodiments that fall within the true scope of theinvention.

With reference to FIGS. 1 a and b, the exciting medium 2, in a preferredembodiment, constitutes a plasma discharge ignited in a regionsurrounding, as in FIG. 1 a, or in a region downstream, as in FIG. 1 b,the source 4 of atomised coating forming material. The substrate 6 withthe surface to be coated is positioned so as to be remote, in this caseby the provision of the physical separation by distance 8, from thelocation of the exciting medium 2.

Suitable plasmas for use in the generation of the exciting medium 2include non-equilibrium plasmas such as those generated by audiofrequencies, radio frequencies (RF), microwaves or direct current. Theplasma can be generated at low-pressure, atmospheric or sub-atmosphericpressures as are known in the art. Of special utility are low-pressureradiofrequency plasmas wherein the gas pressure is 0.01 to 10 mbar andatmospheric-pressure-glow-discharges (APGDs) which typically utilise ahigh flux of carrier gas (usually helium or argon) and a high frequencypower supply (1 kHz to RF).

The plasma can be applied in a continuous or pulsed fashion with the useof pulsed plasmas possibly leading to the yielding of coatings with agreater functional integrity.

An alternative embodiment for providing the exciting medium to excitethe atomised coating forming material prior to deposition is to providea remote plasma 10 as shown in FIG. 2. Species extracted from almost anyplasma, including low pressure RF and MW discharges, hollow cathodedevices and APGDs, can be used to activate and excite the coatingforming material prior to deposition of the same onto the substrate 6.

Other means of creating the reactive precursors to coating depositioninclude, but are not limited to UV/VUV irradiation, electron beamtreatment, y-irradiation, heating (with a grid or lamp) and/or exposureto reactive ground-state species such as ozone (itself for examplegenerated by a remote plasma or UV irradiation). As with plasmas, theabove means of excitation may be continuous or pulsed.

One means for providing a pulsed supply is to use a rotating shutter,although a grid possessing a modulated electrical bias would be capableof intermittently preventing the transit of appropriately chargedspecies.

The following examples illustrate the present invention but are notintended to limit the same.

EXAMPLE 1 Deposition of Hydrophobic/oleophobic Films

1H, 1H, 2H, 2H perfluorooctylacrylate is placed into a monomer 12 tubehaving been purified using repeated freeze-pump-thaw cycles. Coatingdeposition experiments are performed in an apparatus consisting of anultrasonic atomisation nozzle 4 connected to a glass vessel 16, itselfcomprising a radiofrequency plasma excitation generating means 17 andexciting medium volume 2, and a downstream deposition region 14containing the substrate 6 as shown in FIG. 3. The monomer tube isconnected to the ultrasonic nozzle by way of a metering valve 18. Theultrasonic nozzle is itself connected to the glass vessel by way of“nitrile” O-rings 20.

A “Pirani” pressure gauge is connected by way of a Young's tap to theglass reactor vessel. A further Young's tap is connected with theexternal, ambient air supply and a third leads to an Edwards E2M2 twostage rotary pump by way of a liquid nitrogen cold trap 22. Allconnections are grease free.

The exciting medium generating means 16 comprise an L-C matching unitand a power meter are used to couple the output from a 13.56 MHz RFgenerator to a copper coil 19 wound around the wall of the plasmaexciting medium volume 2. This arrangement minimises the standing waveratio (SWR) of the power transmitted from the RF generator to thepartially ionised gas in the plasma excitation volume.

Prior to the deposition of the coating forming material the reactorvessel is soaked overnight in a nitric acid bath, scrubbed withdetergent, rinsed with propan-2-ol and oven dried. The ultrasonicnozzle, metering valve and related fittings are rinsed with propan-2-oland air-dried. The reactor vessel, monomer tube, ultrasonic nozzle,metering valve and related fittings are then incorporated into theassembly shown in FIG. 3. Next the substrate to be coated is placed intothe deposition region 14, downstream of the plasma excitation volume,and the apparatus evacuated to base pressure (7×10⁻³ Torr).

The metering valve is then opened until the liquid monomer flows intothe ultrasonic nozzle at a rate of 8×10⁻⁴ ml s⁻¹. Switching on theultrasonic generator (3.0 W) initiates atomisation of the coatingforming material, resulting in an increase in the chamber pressure to0.4 Torr. The plasma is then ignited and the RF power maintained at 2 W,at which value the plasma is observed to be localised within theexciting medium volume 2 defined by the location of the coils 19.Typically a 0-10 minute deposition duration is used, and found to besufficient to give complete coating coverage of the substrate 6. Afterthis, the metering valve is closed, the RF and ultrasonic generatorsswitched off, and the apparatus evacuated back down to base pressurebefore finally venting to atmospheric pressure.

A spectrophotometer (Aquila Instruments nkd-6000) was used to determinethe thickness of the coatings. Contact angle measurements were made witha video capture apparatus (AST Products VCA2500XE) using sessile 2 uLdroplets of deionised water and n-decane as probe liquids forhydrophobicity and oleophobicity respectively.

The results of 10 minutes of deposition onto silicon wafers inaccordance with the method of this example are shown in Table 1 TABLE 1Deposition Film Contact Coating Forming Duration/ Thickness/ Angle/°Material min nm Water Decane 1H,1H,2H,2H 10 629 ± 55 124 ± 2 73 ± 2perfluorooctylacrylate

In Table 1 it can be seen that the method of the invention enables therapid deposition of relatively thick films from a monomer possessing lowvolatility. The water contact angle results confirm that the films arehydrophobic and the decane contact angles are indicative of a gooddegree of oleophobicity.

EXAMPLE 2 Deposition of a Hydrophilic Coating

In a second illustrative example, the method and apparatus of Example 1and as illustrated in FIG. 3 are repeated using 2-hydroxyethylmethacrylate as the coating forming material.

The hydrophilicity of the deposited coatings are assessed by watercontact angle measurements with a video capture apparatus (AST ProductsVCA2500XE) using sessile 2 uL droplets of deionised water. Informationon the chemical groups present within the films was obtained using FT-IR(Perkin Elmer, Spectrum One).

The water contact angle of coatings deposited onto polished siliconwafers was 28±2°, confirming that they are indeed hydrophilic.

FIG. 4 compares the infrared spectrum of the starting material, 21 withthat of a film deposited onto a polished silicon wafer 23. Absorptionbands indicative of the carbon-carbon double bond in the monomer areabsent in the coating. In contrast, the sought hydroxyl group is shownto be present in both. These results verify that the coating is awell-defined polymer of 2-hydroxyethyl methacrylate, retaining much ofthat monomer's functionality and utility.

EXAMPLE 3 Deposition Using a Remote Microwave Frequency ExcitationSource

In a third illustrative example of the method, described with referenceto FIG. 5, coatings are deposited using an apparatus consisting of anultrasonic atomising nozzle 4 and a remote microwave plasma source 24for generating the exciting medium 2. Activation of the coating formingmaterial 25 is achieved by directing its atomised spray as indicated byarrow 27 into the output of the remote microwave plasma, that being theexciting medium 2. The activated coating precursor species are thenallowed to deposit onto the substrate 6 remote from the exciting medium.The substrate is disposed in a manner that precludes the direct exposureto species incident from the plasma as shown in FIG. 5 in this case bymeans of the distance 8 and the bend 26.

The apparatus is temperature controlled (20-150° C.) and evacuated usingan E2M28 two stage Edwards rotary pump by way of a liquid nitrogen coldtrap 22.

The remote microwave source 24 consists of a quartz cavity connected tothe output of a 2.45 GHz microwave generator by way of a wave-guide. Theopen end of the cavity faces into the excitation medium 2 downstream ofthe ultrasonic nozzle. Process gases are introduced into the cavity incombinations regulated using mass flow controllers 28. A constantreaction pressure is maintained by throttling the rotary pump with abutterfly valve. By interposing a quartz plate 30 between the microwavecavity and the atomised spray it is also possible to deposit coatingsusing only the VUV and UV emission from the plasma to activate thecoating forming material.

Treatment comprises first placing the sample inside the apparatus in asuitable location, away from the deleterious effects of direct exposureto the remote plasma. The apparatus vacuum chamber is then evacuated tobase pressure (4×10⁻³ Tort) before purging with the chosen process gas(or combination of gases) to the selected pressure and allowing thechamber to attain the correct temperature. The coating forming material,purified if necessary with repeated freeze-pump-thaw cycles, is thenintroduced into the atomising nozzle by way of a metering valve 18.Igniting the remote microwave plasma then enables the production of theactivated coating forming material in the exciting medium 2 and itssubsequent deposition onto the substrate 6 located further downstream.Following deposition the microwave generator and ultrasonic nozzle areswitched off, the monomer supply and process gas flows stopped and thechamber evacuated and vented prior to substrate removal.

A spectrophotometer (Aquila Instruments nkd-6000) was used to determinethe thickness of the coatings. The elemental composition and limitedchemical information were obtained using X-ray photoelectronspectroscopy (XPS).

The differences from the prior art of the use of an atomiser, which canbe any of an ultrasonic nozzle, nebulizer or gas jet blast to inject theliquid or liquid/solid slurry into the exciting medium and thepositioning of the substrate to be remote from the exciting mediumwithin the vacuum chamber have provided clearly advantageous coatings.The resultant high flux of coating forming material permits the rapiddeposition of coating material, even from involatile monomers and withthe substrate maintained significantly remote from the exciting medium(typically a plasma) and allows coatings to be formed with specificcharacteristics, such as liquid resistance or permeability at a ratewhich is significantly increased and increased to such an extent as torender the method and apparatus significantly commercially usable andviable.

1. A method for depositing a coating, said method comprising the stepsof: introducing an atomised coating forming material into an excitingmedium in a vacuum chamber, said atomised coating forming materialpassing through the excitation medium and depositing the activatedatomised coating forming material onto a substrate, characterised inthat said substrate is positioned in said vacuum chamber remotely fromthe exciting medium and means for generating the exciting medium so thatthe substrate and coating material applied thereto are substantiallyunaffected by the exciting medium and means for generating the excitingmedium.
 2. A method according to claim 1 characterised in that thesubstrate is remote from the exciting medium in that it is physicallyspaced from the exciting medium by a selected distance and/or a physicalobstacle.
 3. A method according to claim 1 characterised in that thesubstrate is remote from the exciting medium in that a device removesspecies from the exciting medium to prevent the same from reaching thesubstrate.
 4. A method according to claim 3 characterised in that thedevice is an electrically biased or earthed grid positioned between theexciting medium and the substrate.
 5. A method according to claim 1characterised in that additional materials are added to the flow ofatomised coating forming material at, prior to, or subsequent to, thesame passing through the exciting medium.
 6. A method according to claim5 characterised in that said material acts as a buffer to maintainprocess pressure and/or carry the atomized coating forming materialthrough the exciting medium to the substrate.
 7. A method according toclaim 5 characterised in that the additive materials have the additionalcapacity to modify and/or be incorporated into the atomised coatingforming material and/or the resultant coating.
 8. A method according toclaims 5-7 characterised in that to produce a multi-layered coating, theintroduction of the additional material to the atomised coating formingmaterial is pulsed.
 9. A method according to claim 1 characterised inthat the exciting medium is a plasma discharge.
 10. A method accordingto claim 9 characterised in that the exciting medium comprises speciesgenerated from a remote plasma.
 11. A method according to claim 1characterised in that the exciting medium is created by a flux ofelectromagnetic radiation, ionised particles or radicals.
 12. A methodaccording to claim 1 characterised in that the exciting medium isgenerated by a source of highly reactive species such as ozone.
 13. Amethod according to claim 1 characterised in that the exciting medium iscreated by positioning a heat source between the source of atomisedcoating forming material and the substrate.
 14. A method according toclaim 1 characterised in that the exciting medium is pulsed.
 15. Amethod according to claim 1 characterised in that the coating formed onthe substrate is post-treated by exposure to an exciting medium.
 16. Amethod according to claim 1 characterised in that the substrate ispre-treated by exposure to an exciting medium prior to coating.
 17. Amethod according to claim 1 characterised in that the atomised coatingforming material constitutes any or any combination of an organic,organosilicon, organometallic, or inorganic material.
 18. A methodaccording to claim 1 characterised in that the atomised coating formingmaterial is applied through an atomiser.
 19. A method according to claim18 characterised in that the atomiser is an ultrasonic nozzle with asupply of material to the atomiser is as a liquid or liquid/solidslurry.
 20. A method according to claim 18 characterised in that theatomiser used is a nebulizer supplied with the coating forming materialin a liquid or liquid slurry and a carrier gas.
 21. A method accordingto claim 18 chatacterised in that the atomiser is a plain-jet gas blastatomiser supplied with coating forming material in the form of a powder,and a carrier gas.
 22. A method according to claim 1 characterised inthat the atomised coating forming material is introduced into anexciting medium that facilitates the formation of activated precursorspecies to the coating, which precursor species are subsequentlydeposited onto a substrate to form the coating and characterised in thatthe substrate is situated outside of the exciting medium.
 23. A methodaccording to claim 1 characterised in that the exciting medium includesthe atomised coating forming material mixed with an inert or reactivegas.
 24. A method according to claim 1 characterised in that thesubstrate to be coated is positioned with respect to the exciting mediumand means for introducing the coating material such that the coatingmaterial leaves the exciting medium and continues a distance afterleaving the same to apply to the substrate to form the coating thereon.25. A method of producing a multi-layered coating onto a substratesurface, said substrate repeatedly exposed to atomised coating formingmaterial which has passed through an exciting medium and characterisedin that during the repeated exposure, the form of the atomised coatingforming material is changed at least one so as to provide coating layersfrom at least two different forms of atomised coating forming material,26. A method according to claim 25 characterised in that the compositionof the precursor and/or the nature of the exciting medium are changedduring the production of the coating.
 27. Apparatus for the formation ofa coating on a substrate, said apparatus comprising a vacuum chamber,means for holding the substrate in the said chamber, means forintroducing a coating material into the chamber, and means forgenerating an exciting medium within said chamber and characterised inthat the means for introducing the coating material is positioned to beat a first side of the exciting medium location when generated in thechamber and the substrate is positioned to be at the opposing side ofthe said exciting medium location and remote therefrom such that thedirected atomised coating forming material passes through the excitingmedium and, upon leaving the same, passes to the substrate to form thecoating thereon.
 28. Apparatus according to claim 27 characterised inthat the means for generating the exciting medium is spaced from thelocation of the exciting medium within the chamber.